Undead can cower in fear (with a successful Turn Undead, for example) which begs the question: What are they most afraid of, and why?

My reply to it :

Of course they are most afraid, of me, the ham-fisted Cleric, going on their nerves !
And going on their nerves I will !
Just swinging around a little bit with my clubs and my kamas, just showing my kopesh (and not telling them that I'm not proficient with them at all !) - A little scratch of bone here, a small tearing into the unflesh of the zombies …. Cutting off a leg here and turning a wight there … Soon they begin to tremble as my deeds become rumor within the undead community !
Today, I just stepped before Brother Salasso, and i said to him : "Now, Brother Salasso, I will go on your nerves. In fact, I will go so much on your nerves that you will WISH that you were DEAD !"
Of course he kneeled down before me, begged for mercy, but didn't remember anymore where his heart was, that fool ! After further going on his nerves by swinging around my hob-nailed weapons, he finally remembered ! He then showed me the way, directing me to his very heart of hearts !
As soon as I touched it, he gave in to death, with a sigh of relief.
Now that's a cleric work-force as it should be !

— “ Any intelligent fool can make things bigger, more complex, and more violent. It takes a touch of genius – and a lot of courage – to move in the opposite direction.“ (E.F.Schumacher, Economist, Source)